Effect of middle ear modification on umbo vibration. Human temporal bone experiments with a new vibration measuring system.

The effects of aditus blockage, decrease of tympanic cavity volume, and resection of the tensor tympani muscle on umbo displacement were studied in human temporal bones using a new non-contacting video measuring system. This system, combined with stroboscopic illumination, allowed measurement of umbo vibration down to 0.3 micron in the 0.1- to 4.5-kHz frequency range for a constant 124-dB sound pressure level at the tympanic membrane. Aditus blockage caused a mean increase of 5.4 dB with a peak at 2.8 kHz and a mean decrease of 3.4 dB below 1.6 kHz. Decrease of the tympanic cavity volume by 30% to 42% showed an improvement of 2.2 dB in the 1.4- to 3-kHz range and a similar loss below 1 kHz. Resection of the tensor tympani muscle produced a slight improvement of 1.7 dB at 1.8 kHz.